The present invention relates to scrubber machines for cleaning planar substrates and more particularly to a scrubber machine suitable for cleaning printed circuit boards.
With the advent of printed circuit board technology, small and large manufacturers alike have found it expedient to design and produce their own circuit boards which, as is well known, may be mass produced at a fraction of the cost of hand wired circuitry. Typically, in the fabrication of printed circuit boards by one of the well known photo etching or silk screening processes, undesirable copper or silver oxides are formed on the outer surfaces of the circuit board. To ensure a proper electrical connection between the printed circuit and the various component parts subsequently mounted thereon, it is necessary that these oxides be removed from the printed circuit board.
The most widely utilized prior art apparatus for cleaning the surfaces of printed circuit boards has been composed of a plurality of rollers oriented to form a conveyor transport which feeds a printed circuit board beneath a rotating cylindrical brush. The cylindrical brush is preferably formed with a fine dispersion of mineral particles which abrasively remove the oxide and other unwanted matter from the surface of the printed circuit board without damaging the printed circuit itself.
To enhance the finish of the scrubbed surface, a water irrigation system has been utilized to flood the roller as well as the printed circuit board during the cleaning operation. As is well known, this wet brushing process forms a hydroxide coating on the printed circuit board which reduces the subsequent formation of oxides after cleaning, as well as promotes the adherence of solder and electrical components to the printed circuit board.
Although such prior art machines have proven to be a substantial improvement over the hand-polishing pumice-slurry procedures previously utilized, they have serious deficiencies in their general use.
The most significant of these deficiencies have focused on the prior art's relatively large size and high investment cost which has significantly prohibited their widespread use by small manufacturers; their complicated and intricate part designs and mounting configurations which have required an inordinate amount of down time for replacement of worn machine parts; and their limited access to the internal components of the apparatus which has hindered easy cleaning and preventative maintenance upon the machine.
In particular, most of the prior art printed circuit board scrubbers, such as that disclosed in MACA U.S. Pat. No. 3,636,662, have been relatively large and expensive apparatus typically including a rigid free-standing frame which supports a roller conveyor and brush assembly as well as a plurality of heater, blower pump, and motor components. The use of the free-standing frame and auxiliary mounted components has required the user to allocate a substantial amount of floor space within his production facility to the scrubber device, and additionally hard-wire install the device in a permanent location. As will be recognized, such large prior art devices resulted in rather high initial investment and setup costs and additionally significantly inhibited the user from relocating the device at different locations in the plant facility.
Further, the prior art devices typically have been incapable of providing a suitable machine design to facilitate the rapid replacement of both the scrubber brush and conveyor rollers which deteriorate during prolonged use. This particular brush mounting deficiency has been recognized to a limited extent in Martino U.S. Pat. No. 3,795,931, however, due to the rather large and complicated structure disclosed therein, such mounts have not been utilized for mounting both the brush and the roller components. Thus, the majority of prior art apparatus have required the user to expand several hours in disassembling a significant portion of the apparatus to replace both the scrubber brush and conveyor rollers.
Additionally, the prior art scrubber apparatus has heretofore provided only limited access to the internal components of the device. During the scrubbing of the printed circuit board, a substantial amount of oxide dust and dirt particles are liberated from the surface of the circuit board. Although most of this dust and dirt is swept from the machine components by the irrigation system, a small portion often becomes lodged and accumulates in undesirable bearing and contact surfaces. Thus, it is necessary to clean these bearing and roller surfaces periodically during use. However, due to the limited accessibilty and substantial time involved in obtaining access to these components of the prior art machines, the user often failed to perform scheduled preventative maintenance which, after prolonged use, resulted in an overall deterioration or, in extreme cases, complete breakdown of the scrubber device.
Thus, there exists a substantial need for a printed circuit board scrubber which occupies a relatively small space, is portable in nature, facilitates easy replacement of both the scrubbing brush and conveyor rollers, and additionally permits easy access to the internal components of the device.